1. Field of the Invention
This invention relates to novel positive photoresist compositions and to the method for providing positive photoresist layers. In particular the invention deals with .alpha., .beta. diketone-containing polymers as radiation sensitive positive photoresist compositions that have advantageous properties when applied on various substrates. The compositions of the invention are particularly useful in that they provide relatively superior resolution, good adhesion to substrates and good etch resistance.
2. Description of the Prior Art
Photoresists are materials which change their solubility in response to a developer solution after the photoresist has been exposed, such as to ultraviolet radiation. Photoresist compositions may comprise a photo-sensitive compound (hereafter sometimes called sensitizer or photosensitizer), which is blended with a film forming polymeric resin and a solvent. Photoresist compositions may comprise also polymeric materials which of themselves are inherently light sensitive. It is with the latter type, specifically a copolymeric material, that the present invention is concerned. As a consequence of the exposure to radiation of the photoresist, a different solubility rate results between the exposed and unexposed (masked over) portions of a resist film that yields a surface relief pattern after the development. Those photoresists which become more soluble in the exposed regions are referred to as positive photoresists.
The photoresists are applied in any suitable manner, such as by spin coating from an organic solvent or solvent mixture, onto a substrate, such as silicon wafers and chrome plated glass plates. A developer removes the areas of the coated photoresist film that has been exposed to light or other form of irradiation so as to produce a pattern in the photoresist film.
The application of a photosensitive film to various substrates is an essential step in the fabrication of integrated circuits. The substrates are generally silicon wafers which may have a thin oxide coating or other coating such as a silicon nitride or aluminum. The photosensitive film is used to pattern the substrate in a series of steps including exposure, development and substrate etch. It is essential that the mask pattern be accurately reproduced in the substrate etch pattern. To achieve this high degree of accuracy, it is essential that the photoresist film be of uniform thickness, have good adhesion to substrates, good contrast in images formed, and good etch resistance properties.
One of the limitations of materials currently used as commercial photoresists is their lack of sensitivity to light at wavelengths much below 300 nm. The resolution attainable with these resists is typically in the 2-4.mu. range and would be improved were they sensitive to shorter wavelengths of light. There is, therefore, a need for photoresist materials that are sensitive in the deep UV (200-300 nm), i.e. for materials permitting higher resolution and thus a higher information density in the microcircuits manufactured using them. This sensitivity in the deep UV must be accompanied by the other normal attributes of a resist material including good adhesion to substrates, good contrast in images formed, and good etch resistance properties.